U.S. patent number 4,451,801 [Application Number 06/295,905] was granted by the patent office on 1984-05-29 for wideband linear carrier current amplifier.
This patent grant is currently assigned to National Semiconductor Corporation. Invention is credited to Dennis M. Monticelli.
United States Patent |
4,451,801 |
Monticelli |
May 29, 1984 |
Wideband linear carrier current amplifier
Abstract
An amplifier suitable for carrier current line driver
applications is shown. It includes a triangle wave to sine wave
shaper circuit and an automatic level control. It incorporates a
line surge arrestor circuit that is active even when the
transmitting capability is disabled. The circuit is shown in an
integrated circuit form, the output of which is capable of being
boosted by off-chip components.
Inventors: |
Monticelli; Dennis M. (Fremont,
CA) |
Assignee: |
National Semiconductor
Corporation (Santa Clara, CA)
|
Family
ID: |
23139721 |
Appl.
No.: |
06/295,905 |
Filed: |
August 24, 1981 |
Current U.S.
Class: |
330/278; 307/3;
330/129 |
Current CPC
Class: |
H03G
3/3042 (20130101); H03L 5/00 (20130101); H03K
6/02 (20130101) |
Current International
Class: |
H03K
6/00 (20060101); H03K 6/02 (20060101); H03G
3/20 (20060101); H03L 5/00 (20060101); H03F
003/20 (); H04M 011/04 () |
Field of
Search: |
;330/129,278,294,279
;340/31A,31R |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Mullins; James B.
Assistant Examiner: Wan; G.
Attorney, Agent or Firm: Woodward; Gail W. Winters; Paul J.
Pollock; Michael J.
Claims
I claim:
1. An amplifier circuit for supplying a carrier current signal to
an AC power line, said circuit comprising:
a high gain current amplifier having an input, an output and a
current gain n, wherein said amplifier has one stage of phase
inversion, between its input and an output thereof, a series
resistor in said output and a shunt resistor coupled between said
output and said input to provide negative feedback;
an output circuit for coupling said amplifier output to said AC
power line; and
an automatic level control section responsive to the level of
signal at said output and coupled to said amplifier input so that
said level of signal is maintained constant.
2. The amplifier of claim 1 wherein said output circuit includes a
resonant tank circuit tuned to said carrier current signal
frequency.
3. The circuit of claim 1 wherein said automatic level control
section is operated from an inverted NPN transistor having an
emitter coupled through a current limiting resistor to said output
circuit, a collector coupled to said automatic level control
section, and a base coupled to a source of reference potential
whereby said inverted NPN transistor is operated below its
breakdown voltage.
4. The circuit of claim 1 wherein said shunt resistor is ratioed at
n times the value of said series resistor thereby to determine the
numerical value of said amplifier current gain.
5. The circuit of claim 1 wherein said amplifier comprises a common
emitter transistor stage that is coupled to drive a Darlington
amplifier that drives said output circuit and said series resistor
is coupled to the emitter of said Darlington amplifier.
6. The circuit of claim 5 wherein a zener diode is coupled between
said output circuit and the input of said Darlington amplifier
whereby said Darlington amplifier will be turned on when line
surges of said output circuit exceed the breakdown of said zener
diode and said surges will be arrested.
7. The circuit of claim 6 wherein said zener diode is selected to
have a breakdown voltage that is much higher than the normal
operating voltage of said circuit.
8. The circuit of claim 1 further including a sine shaper input
stage coupled to drive said automatic level control section, said
sine shaper being capable of accepting a triangular waveform input
and forming it into a sine wave shape.
9. The circuit of claim 8 wherein said sine shaper input stage
comprises a pair of differentially connected transistors having
degeneration resistors in the emitters thereof.
Description
BACKGROUND OF THE INVENTION
The invention relates to carrier current transmitters, which are
designed to operate into an AC power line. The circuit is designed
to accept a triangle wave signal as described in relation with my
copending patent application titled "Low Temperature Coefficient
Wide Bandwidth Voltage Controlled Oscillator," Ser. No. 289,334,
filed Aug. 3, 1981. This application is incorporated herein by
reference. This oscillator develops a signal at a frequency that is
voltage controlled over a relatively wide range that includes the
most desired carrier current bands. Since the power line presents a
complex impedance, such transmitters must be capable of supplying
substantial power into resistive and/or reactive loads of great
variability.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an amplifier capable of
supplying 300 kHz signal to an AC power line with good
efficiency.
It is a further object of the invention to provide an amplifier
that has a current output, so as to be short-circuit protected and
capable of driving a load of virtually any impedance.
It is still a further object of the invention provide an amplifier
capable of driving an AC power line, and including an active power
line surge arrestor that is active even when the amplifier is
turned off.
These and other objects are achieved in an integrated circuit
configured as follows: A current amplifier is coupled to drive a
tuned circuit load that is coupled to the AC power line. The output
stage includes a zener diode actuated surge arrestor that produces
output transistor conduction when a line surge is present that
exceeds the zener voltage. The current amplifier is driven by an
automatic level control driver that senses the output signal and
adjusts the drive when the output exceeds a predetermined
threshold. The automatic level control is current-driven from a
shaper circuit that accepts a triangular wave input and produces a
sine-wave current drive. Means are provided for disabling the
transmitter signal without impairing the surge arrestor action, and
for boosting the output signal capability with off-chip
components.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a block diagram of the circuit of the invention; and
FIG. 2 is a schematic diagram of an integrated circuit form of the
invention.
DESCRIPTION OF THE INVENTION
FIG. 1 is a block diagram of the transmitter of the invention. The
input is a triangular wave signal applied between terminals 9 and
10. When this signal is passed through shaper stage 11, it produces
a sine wave. The thus produced sine wave signal is applied to one
input of an automatic level control (ALC) circuit 12 which drives
power amplifier 14. Tank circuit 15 is excited by power amplifier
14 so as to produce a sine wave power output signal at terminals 17
and 18 which represent the transmitter output. Capacitor 16 is
chosen to have low impedance at the carrier frequency, but
relatively high impedance at DC and the lower-power line
frequencies (60 Hz). Therefore, terminals 17 and 18 can be
connected to the power lines to provide a carrier current
communications system. The ALC 12 has a second input obtained from
the output signal across tank 15. A capacitor 13 is charged in
proportion to the output peak signal and acts to reduce the signal
transmitted through ALC 12. This creates a negative feedback loop
that acts to maintain the desired output voltage, relatively
independent of the power line signal loading. Full power is applied
to the line only when load conditions warrant it; power is not
wasted.
In effect, under typical conditions, power amplifier 14 operates in
class A and supplies output power at about 35% efficiency.
The circuit of FIG. 12 operates from an 18-volt supply connected
between +terminal 20 and ground terminal 22. A 10-volt supply is
coupled between +terminal 21 and ground terminal 22. As a practical
matter, the 10-volt supply can be obtained from a conventional
on-chip voltage regulator (not shown) operated from the 18-volt
line.
Transistors 25 and 26 are operated as a differential amplifier
(diff amp) driven from terminals 9 and 10. Resistors 28 and 29 act
to degenerate the amplifier whose tail current I.sub.1 is supplied
by transistor 27. Current source 45 passes I.sub.2 through
transistor 44 which operates as a diode due to the coupling created
by transistor 27. Resistor 30a (along with identical resistor 30b)
returns the base of transistor 44 to ground and carries a current
equal to V.sub.BE44 divided by the value of resistor 30a. Resistor
31 is selected relative to the value of resistor 41 so that I.sub.1
is 90% of the current in resistor 30a and I.sub.6 is 110%.
The signal source coupled between terminals 9 and 10 is desirably
obtained at the triangular waveform output of an oscillator of the
kind disclosed in my copending application, Ser. No. 289,334, filed
Aug. 3, 1981. Since this triangular waveform has a peak-to-peak
amplitude of about 2 V.sub.BE, shaper 11 will be driven well into
its nonlinear response regions. Its reduced response at the signal
extremes will convert the triangular input voltage into a sine
waveform of signal current I.sub.3 in the collector of transistor
26. By suitably selecting the values of resistors 28 and 29 along
with the tail current and signal drive, a very close approximation
of a sine wave form can be achieved. I.sub.3 will have upper and
lower peak signal values of about 99% and 1% of I.sub.1 =0.9
V.sub.BE44/R.sbsb.30a.
The collector current, I.sub.3, of transistor 26 flows as tail
current in differentially connected transistors 33 and 34. Current
source 35 passes a reverse current, I.sub.4, through zener diode
36, which operates in reverse breakdown, thereby, to establish a
typical 7 volts at the base of transistor 34.
A current, I.sub.5, flowing in the collector of transistor 37 is
fed into the collector of transistor 34 and is adjusted to slightly
exceed the peak value of I.sub.3. The exact relationship between
I.sub.3 and I.sub.5 is as follows. I.sub.5 is scaled to 86% of
I.sub.6 via the unequal but accurately ratioed resistors 42 and 43
in the current mirror defined by transistors 37, 38, and 39.
I.sub.6 in turn is made a percentage (110%) of
V.sub.BE44/R.sbsb.30a. Thus, I.sub.5 =0.95 V.sub.BE44/R.sbsb.30a.
But I.sub.3 is 1% to 99% of 0.9 V.sub.BE44/R.sbsb.30a or about 0.01
to 0.89 V.sub.BE44/R.sbsb.30a. Therefore, the difference current,
I.sub.5 -I.sub.3, is equal to 0.06 to 0.94 V.sub.BE44/R.sbsb.30a
and flows through breakdown diode, 45, as drive signal current into
the base of transistor 46.
It can be seen that if diodes 36 and 45 have approximately the same
zener voltage, the collector of transistor 34 will always be about
V.sub.BE46 more positive than its base. This avoids any possibility
of saturation in transistor 34 which acts as a signal current
driver, through level shifting diode 45 to drive base signal
current into transistor 46.
If transistor 46 is made to match transistor 44 and if load source
47 produces an I.sub.7 value equal to that of I.sub.2, the V.sub.BE
values of the two transistors will be equal. This means that the
potential at the base of transistor 46 is is the same as the
potential at the base of transistor 44. Feedback forces the
current, 0.06 to 0.94 V.sub.BE44/R.sbsb.30a, the flow through
feedback resistor 48. Because 48 is made equal to 30a, the voltage
dropped across this resistor is 0.06 to 0.94 V.sub.BE44. Relative
to ground (and thus across resistor 49) the potential is equal to
V.sub.BE44 -(0.06 to 0.94 V.sub.BE44) or just 0.06 to 0.94
V.sub.BE44. Since resistor 49 is small relative to 48, the current
through it is large relative to the drive signal of I.sub.5
-I.sub.3 and thus large but controlled current gain results.
Feedback action causes output transistor 52 to conduct this
amplified current and an output voltage proportional to load is
developed in the collector of this device.
Transistor 46 is a high gain inverter which has a capacitor 50
coupled between output and input to create a current driven
integrator. Such frequency compensation introduces a 6 db per
octave roll off of gain with frequency and creates a stable
amplifier configuration. Transistors 51 and 52 are coupled together
to create a Darlington pair which drives tank circuit 15 to produce
an output signal at terminals 17 and 18.
It will be noted that the Darlington pair output emitter drives
resistor 49. Resistor 48 provides negative feedback to the base of
transistor 46. Since the signals at the two ends of resistor 48 are
equal and out of phase, it can be seen that the current gain of the
amplifier that comprises transistors 46, 51, and 52 will be equal
to the ratio of resistor 48 to resistor 49 plus one. With a
resistor ratio of 200 and approximately 300 microamperes peak of
drive signal, a signal current of 60 milliamperes peak will flow in
tank 15 for driving a carrier current line signal. Since a current
drive is used, a too low impedance load will have no ill effect
and, if a too high impedance load is present, the signal voltage at
the collector of transistor 52 will rise and actuate the automatic
level control (ALC) circuit to prevent amplifier saturation and
concomitant signal distortion.
The ALC operates in the following manner. For the conditions
described above, the maximum signal condition is considered.
Capacitor 13 was discharged so as to turn off transistor 33. It
will be noted that resistor 55 couples the collector of transistor
52 (the high impedance point of tank 15) to the collector of
transistor 56. It is to be understood that transistor 56 is
operated in an inverted state. Its normal collector is used as an
emitter and its normal emitter is used as a collector. Thus the
emitter arrow as shown points in the opposite direction to the
actual current flow. The base of transistor 56 is coupled to a
source of reference voltage at terminal 57. Typically this
reference voltage will be about 8 V.sub.BE above ground or at about
4.8 volts. The emitter (actually the inverted collector) of
transistor 56 is coupled to dual collector transistor 58. One
collector of transistor 58 is coupled back to its base so that it
is simply a current mirror. If the two collectors are of equal
size, the current mirror will have unity gain.
It will be noted that with the base of transistor 56 at 4.8 volts
and its emitter (inverted collector) at 9.4 volts, the difference
is only 4.6 volts, which is well below the zener breakdown level.
Since the collector (inverted emitter) of transistor 56 is returned
to the 18 volt supply via resistor 55 it can be seen that a
normally connected transistor 56 could not be used because its
ordinary emitter to base zener breakdown would be exceeded. The
inverted connection avoids this. While an inverted transistor has a
low base to collector current gain, this is not a problem with the
common base connection as shown.
In operation, when the signal at the collector of transistor 52
swings below a level of about 4.2 volts, it will turn transistor 56
on and emitter current will flow in resistor 55. This current pulse
will be mirrored by transistor 58 to charge capacitor 13. As
capacitor 13 charges, at some point it will turn transistor 33 on
and a portion of I.sub.3 will be diverted away from its normal
function of driving transistor 46 via transistor 34. As capacitor
13 charges, its effect will be to reduce signal drive until the
signal swing at the collector of transistor 52 is just barely
sufficient to keep transistor 56 on sufficiently to maintain the
capacitor charge. Base and/or leakage current will normally serve
to discharge capacitor 13. Thus the charge on capacitor 13 will
automatically adjust the signal drive to tank 15 for a constant
signal output voltage even though ambient and load conditions
vary.
Zener diode 60 is coupled to the Darlington pair in such a manner
as to provide a power line surge arrestor action as follows.
Actually diode 60 is a combination or series string of six
emitter-base diodes to give a zener breakdown of about 42 volts. If
a power line surge produces a pulse voltage at the collector of
over about 43 volts, zener diode 60 will start to conduct, thus
turning transistor 51 and hence transistor 52 on. If transistor 52
is constructed to handle a high peak current by the use of plural
emitters suitably ballasted, it will be capable of arresting a
short duration power surge well within its dissipation rating.
Resistor 61 is present to permit the surge arrestor action even if
the transmitter is disabled.
Transistor 63 is the transmitter disable control. Its
collector-emitter parallels that of transistor 46 and its base is
coupled to a disable toggle terminal 64. When disable toggle
terminal 64 is either low or open (in this latter case resistor 65
will pull terminal 64 low) transistor 63 will be off and the
circuit will operate as previously described. However, if terminal
64 is high, transistor 63 will be conductive, thereby pulling the
base of transistor 51 low or off and disabling the transmitter.
However, due to the presence of resistor 61, the surge arresting
capabilities of transistors 51 and 52, as described above along
with zener diode 60, will be intact.
As pointed out above, the circuit as shown in FIG. 2 can supply
about 60 ma (peak current) to tank 15 as a signal source. However,
the presence of pads 66 and 67 provide a boost capability if more
output is desired. Ordinarily pads 66 and 67 are strapped together
by wire 68. If wire 68 is removed, an outboard transistor 69, shown
in dashed outline, can be added. This device would be an NPN high
power transistor preferably with a suitable heat sink mounting for
high current and high power operation. When transistor 69 is
coupled to the circuit, an outboard resistor 70 is added in
parallel with resistor 49. This increases the ratio with resistor
48 and therefore the amplifier current gain. Base pulldown resistor
71 is also added to serve the same function that resistor 62 serves
for transistor 52. Using commercially available transistors, the
output current can be increased by an order of magnitude. To do
this the resistance from pad 67 to ground should be reduced by a
similar factor.
Whereas normally a 0.2 watt output signal is available at terminals
17 and 18, the boosted value is about 2 watts. The surge arresting
capability is also enhanced with boosting but otherwise the circuit
operates as explained above.
EXAMPLE
The circuit shown in FIG. 2 was fabricated in conventional
monolithic silicon form using PN junction isolation. The NPN
transistors were all high current gain devices using vertical
construction. The PNP transistors were all of high current gain
lateral construction. It will be noted that all signal amplifying
stages employ only NPN transistors in order to obtain minimum
signal distortion and overall best performance at 300 kHz. The
following component values were employed:
______________________________________ COMPONENT VALUE UNITS
______________________________________ Capacitor 13 0.1 microfarad
Resistors 28 and 29 410 ohms Resistors 30a and 30b 2K ohms Resistor
31 858 ohms Current Source 35 300 microamperes Resistor 41 1045
ohms Resistor 42 843 ohms Resistor 43 1002 ohms Current Sources 45
and 47 300 microamperes Resistor 48 2K ohms Resistor 49 10 ohms
Capacitor 50 20 picofarads Resistor 55 4K ohms Resistor 61 1K ohms
Resistor 62 2K ohms Resistor 63 100K ohms
______________________________________
The precision values for resistors 31 and 41 are not absolute but
represent a ratio that sets the values of I.sub.1 and I.sub.6. The
same is true of resistors 42 and 43, which determine the ratio of
I.sub.6 to I.sub.5.
A 300 kHz triangular waveform as described was coupled to terminals
9 and 10 and tank 15 was tuned to the same frequency. A 300 kHz
sine wave was present at terminals 17 and 18. Without boosting (no
transistor 69 or resistor 70 and jumper 68 in place) the output
power was about 0.2 watt. The circuit is designed to arrest 0.5 amp
line surges of over 100 volts amplitude for up to 1 ms
duration.
The invention has been described and a working example detailed.
When a person skilled in the art reads the foregoing description,
alternatives and equivalents will become apparent. Accordingly, it
is intended that the scope of the invention be limited only by the
following claims.
* * * * *